organic matter, in comets

Comets contain a rich variety of
organic materials, together with frozen
gases, and refractory grains. Preliminary
analysis of the samples of comet Wild 2 returned to Earth by the Stardust
probe, for example, revealed that about 10% of the comet is made of organic
matter. Since substantial amounts of cometary dust arrived on Earth shortly
after our planet formed, it is at least possible that cometary material
could have played a significant role in prebiotic processes prior to the
appearance of microorganisms.